Research studies performed by Lawrence Livermore National Laboratory, Massachusetts Institute of Technology, and others have confirmed that joints using Spiralock threads carry load much more uniformly than ones with standard 60° threads. Additionally, they show that the percentage of load on the first engaged thread produced with a Spiralock tap is significantly lower, 24% versus 64%, with five threads of engagement.
Standard 60° Thread
The uniform thread loading provided by Spiralock reduces the load concentration at the first engaged thread, thereby improving joint reliability by minimizing the likelihood of thread stripping. Additionally, the Spiralock thread form generates higher radial thread loading compared to standard threads, thus taking advantage of the material hoop strength and lowering the chance of shear failure.
The unique 30° wedge ramp in the Spiralock thread form contacts the male threads at a different angle than standard threads do. A greater portion of the assembly forces are redirected from an axial direction to a radial direction to create the locking capability, so Spiralock threaded joints generally require 10% to 20% more torque to generate equivalent joint tension as a standard 60° thread.
Although higher torque is required in all Spiralock threaded joints, the increase in required torque will vary depending on the types of materials and coatings being used (nut, bolt, mating surfaces, etc.). This torque/tension relationship should be evaluated in the actual joint to determine the proper torque required to develop the specified tension.
Testing performed by the Goddard Space Flight Center has shown that Spiralock offers a consistent pattern of friction, especially when the threads are lubricated. Spiralock’s more consistent friction factor directly relates to a more consistent joint tension or preload.
Testing performed on ¼”-28 Spiralock fasteners in conjunction with NAS624-32 bolts has shown that Spiralock can enhance fatigue life 300% over standard fasteners. The even load distribution with Spiralock consistently reduces the stress concentration that leads to fatigue failures.